Bacterial mutants were isolated that allow chromosome inversion of non- permissive chromosome intervals. It is not known why some intervals are non-permissive, the phenomenon could be due to some aspect of chromosome folding or local supercoiling. One of the major differences between prokaryotes and eukaryotes is the way they package DNA and deal with DNA twisting (toroids vs supercoils) and this difference is fundamental to comparisons of gene expression in euks and proks. This fundamental difference may ultimately be the basis of designed antibiotics that affect twisting, folding and segregation of nucleoids since the bacterial targets have this as a unique feature that is absent from euks. The aim of the postdoctoral work. a) Look for mutations in which non-permissive intervals can invert, and characterized those mutants. b) Make a random screen of "second endpoint" in inversions at different places in the chromosome.